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2006 R18A
3-stage VTEC
Examine the SOHC VTEC and SOHC VTEC-E implementations. The clever Honda engineers saw that it is a logical step to merge the two implementations into one. This is in essence the 3-stage VTEC implementation. 3-stage VTEC is implemented on the R18A 1.8 SOHC engine in which the VTEC-E mechanism is combined with the power VTEC mechanism.
Many of us probably has laughed at the poor ignorant layman who said "I want power AND economy from my Honda". We know of course that power and economy are mutually exclusive implementations. Honda decided not to abide by this rule. Now, with 3-stage VTEC, we get BOTH power and economy !.
The diagram below illustrates the 3-stage VTEC implementation. The intake rocker arms have two VTEC pin actuation mechanisms. The VTEC-E actuation assembly is located above the camshaft while the VTEC (power) actuation assembly is the standard wild-cam lobe and rocker assembly.
Below 3500rpm and with gentle accelerator pressure, neither pin gets actuated. The engine operates in 12V mode with very good fuel combustion efficiency. When the right foot gets more urgent and/or above 3500rpm, the upper pin gets actuated. This is the VTEC-E mechanism at work and the engine effectively enters into the '2nd stage'. Now R18A 3-stage works in 16V mode (both intake valves works from the same mild cam-lobe).
Stage 2 operates from around 3500rpm to 5200rpm. When the rpm exceeds 5200rpm, the VTEC mechanism activates the wild cam-lobe pushing the engine into the '3rd stage', the power stage. Now the engine gives us the full benefit of its 140ps potential !
The 3-stage I-VTEC R18A engine is used on the current 8th generation Civic. The 3500rpm cutover from lean-burn to normal 16V operation in fact varies according to load and driver requirements. With gentle driving, lean-burn can operate up to 3500rpm or higher. The essence of 3-stage I-VTEC is power AND economy implemented on a 1.8l SOHC PGM-Fi engine. Many people mistake 3-stage I-VTEC as a "superior" evolution of the power oriented DOHC VTEC implementation, describing DOHC VTEC as "the older 2-stage VTEC" and implying an inferior relationship. This is totally wrong because DOHC VTEC is tuned purely for high specific output and sports/racing requirements. 3-stage I-VTEC is in truth an evolution of SOHC VTEC and VTEC-E, merging the two implementations into one.
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Let me also add some personal thoughts. Over the last decade or so Automatic transmissions have improved out of sight & these days it is not uncommon to see an Auto returning better fuel economy than a manual (on the same model car)
As we are talking about an FD1 lets do a simple comparrison. At 100KPH in an Auto the engine is spinning over @ about 1800RPM whereas in the manual it is doing about 2700RPM. Therefore your injectors on the manual are pumping in more fuel at the same road speed, admittedly only a small amount, but it adds up over time. The only disadvantage with the auto in highway cruising is it only has to sniff an incline or slight hill & it will drop back a gear. This can be very annoying to some people, but they fail to realise that there is insufficient torque at that RPM to tackle any sort of incline.
In these days of ridiculous fuel prices I believe it pays substantial dividends to learn to drive economically & there is an art to it that is difficult to learn for some. It is not necessarily a matter of driving slower, but leaning how to do it. A classic case is when my wife drives our CU2 Auto she uses about 3L/100k more than I do, yet I am the faster driver. Go figure that 1.
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 Originally Posted by JOhnnyFD
LMFAO, you had the links, so why did you ask me to explain?
I didn't have the links, just the articles that I had saved.
If anyone wants a copy of my spreadsheet for an FD1 Auto from new to 60K, just pm me your email add.
Last edited by buddah51au; 20-11-2009 at 05:44 PM.
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lol.. wot??.. i didnt ask anything buddah.. i think u must have misinterpreted me.. i was sayin in previous posts.. that i was explainin VTEC in regards to fuel consumption.. not really askin to explain VTEC.. i just summed it up b4
my bad if uve misinterpreted it
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no probs mate, I probably misinterpreted as I dont frequent the FD forum much now as i have moved up to a Euro. I thought My FD1 was good on fuel - 6.78 average over 60,000km, but the Euro is more amazing 7.16 over 20,000km
Last edited by buddah51au; 20-11-2009 at 06:50 PM.
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i just got to 600.1 km and still got 1 bar left + the reserve fuel once all the bars go  and i used air-con A LOTT
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You're crazy. Lots of highway driving for you?
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600km is good, but i found it to be the norm, 600 was when my low fuel light came on. anything under that was very rare. my best ever was 708km on 44.5 lts. However my best consumption was 577km on 34.4 lts.
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my usual is abour 550 when the light comes on
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hardly any highway, trips from my house to go out and eat etc max 30min trips on normal roads with lots of air-con.. was mid 30's outside other day zzz so hott
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450kms full tank... combine cycle..... just running 1000km
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